The present invention relates to a method and an apparatus for recording and/or reproducing information on or from an information recording medium such as an optical disk, a magnetic disk, a magnetooptical disk and others. More particularly, the present invention is concerned with the information recording/reproducing method and apparatus capable of recording and/or reproducing information on or from the recording medium along record tracks with an enhanced accuracy by using a sampling servo type tracking system and which are profitably suited for the information recording and/or reproduction on or from an erasable recording medium susceptible to overwriting of information such as typified by a magnetooptical disk or the like media.
As a means for tracking the information recording tracks in the prior art information recording/reproducing systems such as optical disk apparatuses, magnetic disk apparatuses and others, there is known a sampling servo type tracking system in which marks for detecting a tracking signal are previously formed on the recording medium intermittently along the track in the form of so-called prepits, wherein data are recorded in the recording areas defined between the prepits. For further particulars, reference may be made, for example, to U.S. Pat. No. 4,364,118.
In recent years, reversible recording media have been developed for use in the optical disk apparatus. Among them, an overwritable (erasable) recording medium attracts attention. In particular, promising is the magnetooptical recording medium which permits the overwrite operation under application of the magnetic field modulated with the data signal to be recorded. A typical one of the overwritable disk systems operative through application of the modulated magnetic field is proposed, for example, in Japanese Patent Publication JP-B-60-48806.
When an optical disk apparatus is to be implemented by adopting both the sampling servo type tracking system and the magnetic field modulation overwrite system, it is necessary to modify or rearrange the tracking system as well as the track access system and the data recording/reproducing system so that the optical disk apparatus can carry out these various operations in an integrated manner. Heretofore, however, no proposal has been made in connection with the optical disk apparatus of such integrated structure because of problems remaining to be solved, such as mentioned below.
(1) In the sampling servo type tracking system, any possible defect of the tracking signal detection marks (prepits) will involve remarkable disturbance in the tracking servo signal, exerting very adverse influence to the tracking performance.
(2) Since the overwritable magnetooptical recording medium is employed, wherein the recording on the medium can only be carried out by resorting to the use of thermal energy of a light spot and at the same time a modulated magnetic field pulse signal, the magnetized domains (or data domains) as formed on the disk by the magnetooptical recording tend to deviate temporally from the recording (magnetic field) pulses.
(3) Because the amount of prepit signals such as the tracking signal detection mark signal, header information signal and others is great when compared with that of the magnetooptical signal representative of the record information (i.e. information to be recorded or reproduced), the prepit signal may leak into the information or data signal to thereby interfere with the latter.
(4) Means is required for detecting the wobbling phase of the meandering row of the tracking signal detection marks or prepits with high reliability.
(5) For realizing the track access operation, there is required a means for detecting the positional information of the information recording/reproducing means such as a light spot focussing system relative to the recording medium.